Stent effects on duplex velocity estimates.

Background: Doppler-derived velocity criteria used to define the presence and severity of in-stent restenosis after percutaneous angioplasty and endoluminal stenting have been called into question. This study uses an in vitro flow model to examine Doppler-derived velocities after placement of balloon-expandable and self-expanding endoluminal stents (BES and SES).

Methods: An in vitro vascular circuit model consisting of a pulsatile pump, tubing, and a conduit was created. The pump was programmed to replicate the Doppler spectral waveform pattern of the renal and carotid arteries. Peak systolic velocity (PSV) and end diastolic velocity (EDV) were estimated at five distinct conduit locations. Three replicate velocity measurements were made at each location. After initial velocity estimates, a BES or an SES was deployed within the conduit.

Results: Mean ± standard error PSV was 95.8 ± 2.6 cm/s, 97.0 ± 2.7 cm/s, and 101.4 ± 2.7 cm/s for unstented, BES and SES, respectively. PSV estimates were increased between unstented and stented conduits when SESs were present. The increase in mean systolic velocity of 6.4% observed with SES was statistically significant (P < 0.05). EDV values did not differ significantly across conditions. Mean ± standard error EDV was 36.2 ± 1.0 cm/s, 37.3 ± 1.1 cm/s, and 37.2 ± 1.1 cm/s for unstented, BES, and SES, respectively.

Conclusion: The presence of an SES was associated with a less than 7% change in estimated PSV. These results suggest that Doppler velocity estimates for renal and carotid arteries are not materially affected by either BES or SES.